At the end of Basic rules section, we did Practice 1, but we couldn't finish it with basic knowledges.
You have learned new rules in this "General rules" section. So let's try the rest of practice 1 to see how much you've made a progress.
The following is where we stopped in Practice 1.


First you can apply the rule of "Drawing a line to a corner of 3" here.


There are diagonal "2s" in the upper left of that "3". You can apply the rule of "Diagonal 2s".


Lines will be drawn easily and the Lshape line will be connected with another lines around "3". And you can draw the last line for that "3".
Again you can use the rule of "Drawing a line to a corner of 3" at star marked vertex.


Now you can use the rule of "Diagonal "32..23" here.


Obviously you cannot draw a line on edge "a". If you do, you will make a closed loop with only two faces. This conflicts with the rule.
Since the edge "a" cannot have a line, some of other edges will be decided automatically.


And this decides some other edges.


And the rest of upper right area of this puzzle will be solved.


The two lines on the right and left edges of the right "2" must go down, connecting with the lines around lower "3".
And the remaining edge will be decided automatically.
Now you can use the rule of "Drawing a line to a corner of 1" here.


Since a line will be drawn toward "1" on the left or bottom edge of star marked vertex, there will be a line on either the left or bottom edge of "1". Therefore, "x" will be marked on the top and right edges of "1".


Then you can draw lines around "3" and above "2".
Now, look at edge "b". See how the lines go from the two ends of edge "b".
You will see the lines are making one loop. You cannot close this loop here. So mark the edge "b" with "x".


Then two lines will be drawn on the right and left edges of "2". You don't need any more explanation to finish up the loop, do you?
I have just demonstrated that gerenal rules are enough to solve this level of puzzles.
I can guarantee now you can solve Level 2 problems (**).
Also, you should be able to try Level 3 problems (***).